GENERAL MICROBIOLOGY - T.P. Pirog - 2004

13. BIOSYNTHETIC PROCESSES IN MICROORGANISMS

13.5. FORMATION OF CARBOHYDRATES — CELL WALL COMPONENTS

If Glucose serves as the substrate, its catabolic products include glucose-6-phosphate, fructose-6-phosphate, and fructose-1,6-diphosphate, while the Pentose Phosphate Pathway yields ribulose-5-phosphate, xylulose-5-phosphate, and ribose-5-phosphate. When non-carbohydrate substrates are used, CARBOHYDRATES such as glucose-6-phosphate, fructose-6-phosphate, and fructose-1,6-diphosphate are synthesized via Gluconeogenesis. The interconversion of Monosaccharides occurs through nucleoside diphosphate sugars (for example, via UDP derivatives).

As an example, let us examine The Biosynthesis of individual Cell wall components in the Gram-negative bacterium E. coli.

One of the precursors of the E. coli cell wall lipopolysaccharide is UDP-galactose, which is formed from glucose-6-phosphate:

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The second precursor of The Cell wall lipopolysaccharide consists of hexosamines, which are derived from fructose-6-phosphate. Fructose-6-phosphate is converted into glucosamine-6-phosphate using glutamine as an amino group donor:

Other hexosamines are synthesized from glucosamine-6-phosphate.

UDP-N-acetylmuramic acid and UDP-N-acetylglucosamine—the precursors of peptidoglycan—are also synthesized from glucosamine-6-phosphate (Fig. 13.6). First, the phosphate group is transferred from position 6 to position 1 to yield glucosamine-1-phosphate. A subsequent reaction with acetyl-CoA produces N-acetylglucosamine-phosphate, which then binds to UDP. In the final step, UDP-N-acetylglucosamine reacts with phosphoenolpyruvate to form UDP-N-acetylmuramic acid.

The building block of peptidoglycan is UDP-N-acetylmuramyl pentapeptide. The pentapeptide is synthesized from UDP-N-acetylmuramic acid through a series of sequential reactions involving L-Alanine + ATP, D-glutamate + ATP, meso-diaminopimelate + ATP, and D-alanyl-D-alanine + ATP.